The present invention is related to an apparatus for the linear acceleration of protons for proton-therapy.
Proton-therapy is a type of particle therapy which uses a beam of protons to irradiate diseased tissue, most often in the treatment of cancer. The main advantage of proton therapy is the ability to more precisely localize the radiation dosage when compared with other types of external beam radiotherapy.
In the past and present, several technical approaches have been pursued for the accelerator that produces the proton beam. Mainly circular accelerators, like cyclotrons (or synchrocyclotrons) and synchrotrons have been used.
Also different types of accelerators have been proposed like linear accelerators, and they are currently under development at some research centers (Italy, CERN).
One of the main problems against the diffusion of proton-therapy is related to the cost of the facility. Despite the undoubtedly superior quality of the proton treatment vs the X-rays radiotherapy, the difference in costs between a proton-therapy installation and the best X-rays installation is still too high to permit a wide diffusion of the proton-therapy treatment.
The cost of a proton-therapy installation is strictly related to the facility layout. The accelerator cost covers only a small portion (usually around 20-30%) of the general cost, the main part being due to infrastructures, building, shielding and electricity.
The major drawback of the circular accelerators for their use in proton-therapy facilities is due just to the plant layout required, and especially to the heavy shielding required by the operation of those accelerators. These accelerators usually lose high energy particles that generate stray radiation to the environment (neutrons and X-rays).
In cyclotrons and synchrocyclotrons a particle is accelerated in circles to the desired energy and then ejected out of the machine by an extraction process whose efficiency is not larger than 70%. So some high energy beam is left inside the accelerator. Circular accelerators are very heavy machines, with weights of the order of 200 to 500 tons and with diameter range from 2 to 6 meters depending if built with superconducting coils or normally conducting coils. The beam energy is fixed to the maximum allowable energy so that to irradiate patients with a lower energy an external degrader has to be used. This, at the same time degrades also the beam quality, in such a way that an emittance filter is needed that transmits only 70%-10% of the generated current, depending on the energy degradation parameters.
In contrast to circular accelerators, linear accelerators known also as “linac” do not circulate the particle, but the particles go through a series of resonant cavities disposed linearly.
A linear accelerator is composed of two essential elements: the resonator, having a function of accelerating the particles; and the focusing system which is used to contain and confine the particle beam.
The main advantages of a linac for the application in proton-therapy consist in the accelerator dimension which is rather small in the transverse dimensions while it expands in the longitudinal dimension.
Moreover in a linac the particle transmission from the lowest to the highest energy can be virtually without particle losses. These two features combine fruitfully so to have an accelerator that can be easily shielded simplifying radio-protection requirements.
U.S. Pat. No. 4,392,080 discloses a linear particle accelerator.